Navigation

转载

mb5fe18e9fef50b 2021-08-23 17:07:00

文章标签 android xml ide bundle java 文章分类 后端开发

Navigation

基本操作

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="409dp"
        android:layout_height="729dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/my_nav_graph" />
</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.example.mynavigation;

import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.NavigationUI;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 要先把xml里的组件名称由androidx.fragment.app.FragmentContainerView改成fragment
        NavController controller = Navigation.findNavController(this, R.id.fragment);
        NavigationUI.setupActionBarWithNavController(this, controller);
    }

    @Override
    public boolean onSupportNavigateUp() {
        NavController controller = Navigation.findNavController(this, R.id.fragment);
        return controller.navigateUp();
    }
}

fragment_home.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".HomeFragment">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.5" />

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Home"
            android:textSize="34sp"
            app:layout_constraintBottom_toTopOf="@+id/guideline2"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.8" />

        <Button
            android:id="@+id/btn_home"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline2"
            app:layout_constraintVertical_bias="0.2" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</FrameLayout>

HomeFragment.java

package com.example.mynavigation;

import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class HomeFragment extends Fragment {


    public HomeFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_home, container, false);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        getView().findViewById(R.id.btn_home).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 界面跳转
                NavController controller = Navigation.findNavController(view);
                controller.navigate(R.id.action_homeFragment_to_detailFragment);
            }
        });
    }
}

fragment_detail.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".DetailFragment">

    <!-- TODO: Update blank fragment layout -->

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.5" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Detail"
            android:textSize="34sp"
            app:layout_constraintBottom_toTopOf="@+id/guideline3"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.8" />

        <Button
            android:id="@+id/btn_detail"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline3"
            app:layout_constraintVertical_bias="0.2" />
    </androidx.constraintlayout.widget.ConstraintLayout>

</FrameLayout>

DetailFragment.java

package com.example.mynavigation;

import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class DetailFragment extends Fragment {

    public DetailFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_detail, container, false);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        getView().findViewById(R.id.btn_detail)
                .setOnClickListener(Navigation.createNavigateOnClickListener(R.id.action_detailFragment_to_homeFragment));
    }
}

my_nav_graph.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/my_nav_graph"
    app:startDestination="@id/homeFragment">

    <fragment
        android:id="@+id/detailFragment"
        android:name="com.example.mynavigation.DetailFragment"
        android:label="Detail"
        tools:layout="@layout/fragment_detail">
        <action
            android:id="@+id/action_detailFragment_to_homeFragment"
            app:destination="@id/homeFragment"
            app:enterAnim="@android:anim/fade_in" />
    </fragment>
    <fragment
        android:id="@+id/homeFragment"
        android:name="com.example.mynavigation.HomeFragment"
        android:label="Home"
        tools:layout="@layout/fragment_home">
        <action
            android:id="@+id/action_homeFragment_to_detailFragment"
            app:destination="@id/detailFragment"
            app:enterAnim="@android:anim/slide_in_left" />
    </fragment>
</navigation>

转场传值和动画效果

my_nav_graph.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/my_nav_graph"
    app:startDestination="@id/homeFragment">

    <fragment
        android:id="@+id/homeFragment"
        android:name="com.example.mynavigation2.HomeFragment"
        android:label="fragment_home"
        tools:layout="@layout/fragment_home" >
        <action
            android:id="@+id/action_homeFragment_to_detailFragment"
            app:destination="@id/detailFragment"
            app:enterAnim="@anim/slide_from_left" />
    </fragment>
    <fragment
        android:id="@+id/detailFragment"
        android:name="com.example.mynavigation2.DetailFragment"
        android:label="fragment_detail"
        tools:layout="@layout/fragment_detail" >
        <argument
            android:name="name"
            app:argType="string"
            android:defaultValue="haha" />
    </fragment>
</navigation>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/fragmentContainerView"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/my_nav_graph" />
</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.example.mynavigation2;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

fragment_home.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".HomeFragment">

    <!-- TODO: Update blank fragment layout -->

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Home"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/edt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="请输入"
        android:inputType="textPersonName"
        android:minHeight="48dp"
        android:text="Name"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.895" />

</androidx.constraintlayout.widget.ConstraintLayout>

HomeFragment.java

package com.example.mynavigation2;

import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.Toast;


public class HomeFragment extends Fragment {

    public HomeFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_home, container, false);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        getView().findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                EditText editText = getView().findViewById(R.id.edt);
                String str = editText.getText().toString();
                if (TextUtils.isEmpty(str)){
                    Toast.makeText(getActivity(), "请输入内容", Toast.LENGTH_SHORT).show();
                    return;
                }

                Bundle bundle = new Bundle();
                bundle.putString("input", str);

                NavController controller = Navigation.findNavController(view);
                // 可以传递转场动作的id或者转场目的地的id
                controller.navigate(R.id.action_homeFragment_to_detailFragment, bundle);
            }
        });
    }
}

fragment_detail.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".DetailFragment">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

DetailFragment.java

package com.example.mynavigation2;

import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class DetailFragment extends Fragment {

    public DetailFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_detail, container, false);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        TextView textView = getView().findViewById(R.id.textView);
        String str = getArguments().getString("name");
        String str2 = getArguments().getString("input");
        textView.setText(str2);
    }
}

slide_from_left.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <translate
        android:fromXDelta="-100%"
        android:toXDelta="0%"
        android:duration="1000"/>
</set>

使用viewmodel和databinding

依赖

implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

dataBinding{    enabled true}

将xml改成databing风格才会自动生成binding类
nav_graph.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_graph"
    app:startDestination="@id/masterFragment2">
    <fragment
        android:id="@+id/masterFragment2"
        android:name="com.example.mynavigation3.MasterFragment"
        android:label="fragment_master"
        tools:layout="@layout/fragment_master" >
        <action
            android:id="@+id/action_masterFragment2_to_detailFragment3"
            app:destination="@id/detailFragment3" />
    </fragment>
    <fragment
        android:id="@+id/detailFragment3"
        android:name="com.example.mynavigation3.DetailFragment"
        android:label="fragment_detail"
        tools:layout="@layout/fragment_detail" >
        <action
            android:id="@+id/action_detailFragment3_to_masterFragment2"
            app:destination="@id/masterFragment2" />
    </fragment>
</navigation>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragmentContainerView"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="409dp"
        android:layout_height="729dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/nav_graph" />
</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.example.mynavigation3;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

fragment_master.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="data"
            type="com.example.mynavigation3.MyViewModel" />

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MasterFragment">

        <TextView
            android:id="@+id/tv1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(data.number)}"
            android:textSize="34sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.358" />

        <Button
            android:id="@+id/btn_next"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="下个页面"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.612" />

        <SeekBar
            android:id="@+id/seekBar"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:max="10"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

MasterFragment.java

package com.example.mynavigation3;

import android.os.Bundle;

import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.lifecycle.ViewModelProviders;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.SeekBar;

import com.example.mynavigation3.databinding.FragmentMasterBinding;

public class MasterFragment extends Fragment {

    public MasterFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        MyViewModel myViewModel;
        myViewModel = ViewModelProviders.of(getActivity()).get(MyViewModel.class);
        FragmentMasterBinding binding;
        binding = DataBindingUtil.inflate(inflater, R.layout.fragment_master, container, false);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(getActivity());

        binding.btnNext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                NavController controller = Navigation.findNavController(view);
                controller.navigate(R.id.action_masterFragment2_to_detailFragment3);
            }
        });
        binding.seekBar.setProgress(myViewModel.getNumber().getValue());
        binding.seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
                myViewModel.getNumber().setValue(i);
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });


        return binding.getRoot();
//        return inflater.inflate(R.layout.fragment_master, container, false);
    }
}

fragment_detail.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="data"
            type="com.example.mynavigation3.MyViewModel" />

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".DetailFragment">


        <TextView
            android:id="@+id/tv2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(data.number)}"
            android:textSize="34sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.31" />

        <Button
            android:id="@+id/btn_add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+"
            android:onClick="@{()->data.add(1)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.208"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/btn_minus"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="-"
            android:onClick="@{()->data.add(-1)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.782"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.499" />

        <Button
            android:id="@+id/btn_previous"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="上个界面"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.501"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.653" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

DetailFragment.java

package com.example.mynavigation3;

import android.os.Bundle;

import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.ViewModelProviders;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.mynavigation3.databinding.FragmentDetailBinding;

public class DetailFragment extends Fragment {

    public DetailFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        MyViewModel myViewModel;
        myViewModel = ViewModelProviders.of(getActivity()).get(MyViewModel.class);
        FragmentDetailBinding binding;
        binding = DataBindingUtil.inflate(inflater, R.layout.fragment_detail, container, false);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(getActivity());

        binding.btnPrevious.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                NavController controller = Navigation.findNavController(view);
                controller.navigate(R.id.action_detailFragment3_to_masterFragment2);
            }
        });
        return binding.getRoot();

//        return inflater.inflate(R.layout.fragment_detail, container, false);
    }
}

MyViewModel.java

package com.example.mynavigation3;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class MyViewModel extends ViewModel {
    private MutableLiveData<Integer> number;

    public MutableLiveData<Integer> getNumber() {
        if (number == null){
            number = new MutableLiveData<>();
            number.setValue(0);
        }
        return number;
    }

    public void add(int n){
        if (number.getValue() < 0){
            number.setValue(0);
        } else {
            number.setValue(number.getValue() + n);
        }
    }
}

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